Opinions on Rega Apheta 3 or 2?

You have definitely talked me off ZYX cartridges. I will look into the other mentions you've laid out.

If you want to have warranty and LOMC - you can go for Yatra why not but better one is not H version. If you have capable phono stage it will be good.
It's interesting cartridge and craftsmanship of ZYX is really good one.

As about shims if you will buy cartridge with advanced profile you have to use shims. Of course as Rega tonearm don't have VTA adjustment it's tricky.

Yatra and others are all discontinued old models, you can check on their site. I think Monster Cable cartridges are better than low range of discontinued ZYX. Nakatsuka-San designed Monster Cable cartridges before he formed ZYX. Regarding ZYX you can seach this forum and you will find why it is a problematic: suspension fails before stylus wear off, sealed cartridge body is a nightmare for re-tippers when you have to replace the cantilever, special construction of the cantilever is also very problematic for re-tippers when you want to glue new stylus. ZYX does not support grey market products, and discontinued models cannot be replaced with new models (if they are not from the official dealer), they do not re-tip/refurbish, they can only replace the whole cartridge, but for crazy price.

There are tons of better cartridges on the market (especially vintage MM,MI or LOMC).
it depends on your budget, some killer MM are under $700 and there are plenty of them NOS, some exceptional MM with exotic materials are under $1.2k and those are simply the best even in comparison to the $3k LOMC

Regarding VTA adjustment, maybe you don’t even need to change anything, it depends on the cartridge, you can figure out when you will screw it in and put the needle on the record. If tonearm is not parallel to the record surface (when the needle is in the groove) then you can add spacer between the cartridge and tonearm. The difference will be very small anyway and that spacer is very thin. Positive VTA is acceptable according to Mr. Van den Hul interview (can;t find the link now) and it can improve high frequency resolution. Negative VTA is probably not acceptable, but it rarely happens. I think you can adjust almost any cartridge on your tonearm with spacers (or without them).

Rega does not made their tonearm exclusively for their own cartridge, most cartridges are standard.

A cartridge with replaceable stylus is what you need, you can experiemnt with different profiles on the same cartridge boby (it must be MM or MI/IM). Grace is the best, because many different styli available, not only original, but also from SoundSmith (direct replacement). I prefer the original for LEVEL II

I have tried the ZYX Bloom III with a Planar 8. Although the sound quality is very good, there is an unacceptable hum (doesn't matter whether the motor is on or off) that I can not resolve. Also (very dry in AZ), on some records, there is an occasional loud static discharge pop (every couple minutes). I have never experienced this with any other table/cartridge combination.